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| #include<bits/stdc++.h>
#define int long long
#define ull unsigned long long
#define maxn 100005
#define put() putchar('\n')
#define Tp template<typename T>
#define Ts template<typename T,typename... Ar>
using namespace std;
Tp void read(T &x){
int f=1;x=0;char c=getchar();
while (c<'0'||c>'9') {if (c=='-') f=-1;c=getchar();}
while (c>='0'&&c<='9') {x=x*10+c-'0';c=getchar();}
x*=f;
}
namespace Debug{
Tp void _debug(char* f,T t){cerr<<f<<'='<<t<<endl;}
Ts void _debug(char* f,T x,Ar... y){while(*f!=',') cerr<<*f++;cerr<<'='<<x<<",";_debug(f+1,y...);}
#define gdb(...) _debug((char*)#__VA_ARGS__,__VA_ARGS__)
}using namespace Debug;
#define fi first
#define se second
#define mk make_pair
const int mod=1e9+7;
int power(int x,int y=mod-2) {
int sum=1;
while (y) {
if (y&1) sum=sum*x%mod;
x=x*x%mod;y>>=1;
}
return sum;
}
int n,a[maxn],s[maxn],ans,g[maxn];
signed main(void){
int i;
read(n);
for (i=1;i<=n;i++) read(a[i]),s[i]=s[i-1]+a[i];
for (i=1;i<=n;i++) g[i]=s[i];
sort(g+1,g+n+1);
int tot=unique(g+1,g+n+1)-g-1;
if (g[1]<=0) return puts("-1"),0;
if (tot!=n) return puts("-1"),0;
for (i=1;i<=n;i++) s[i]=lower_bound(g+1,g+1+n,s[i])-g;
if (s[n]!=n) return puts("-1"),0;
for (i=1;i<n;i++) while (s[i]!=i) swap(s[s[i]],s[i]),ans++;
printf("%lld\n",ans);
return 0;
}
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